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STANDARD ATTRIBUTES(5)	 BRL-CAD Standard Conventions	STANDARD ATTRIBUTES(5)

NAME
       gattributes - standard attribute	conventions in BRL-CAD databases

BACKGROUND
       Starting	with BRL-CAD database format version 5,	BRL-CAD	supports the
       storage of arbitrary attribute/value data on any	database object. Prior
       to the development of this generic ability, BRL-CAD supported a set of
       standard	attributes used	to hold	key information	about specific
       properties. These conventions predate not only the version 5 database
       format but BRL-CAD itself. The purpose of this man page is to identify
       the standard attributes,	document situations where two or more
       attributes are used to identify the same	property, and identify where
       appropriate what	constitutes meaningful values for an attribute.

       The earliest ancestor of	BRL-CAD	was the	MAGIC code, written by the
       Mathematical Applications Group,	Inc in 1967 to implement geometric
       modeling	ideas developed	by BRL and AMSAA from 1958-1967. That system,
       which was entirely non-graphical, was followed some years later by the
       GIFT program - Geometric	Information From Targets. LIBRT, appearing
       around 1983, became the successor to GIFT. Today	it is the core library
       of the BRL-CAD solid modeling package. (For more	background see
       http://ftp.arl.army.mil/~mike/papers/96thebook/). LIBRT inherited both
       geometric primitives and	attributes from	GIFT - this heritage is
       occasionally apparent in	attribute names.

       Note that with the introduction of support for arbitrary
       attribute/value pairs, it becomes much simpler for both developers and
       users to	formulate new standards	of their own for storage of metadata
       in attributes. Attributes should	only be	documented in this file	if one
       or more core BRL-CAD tools has implemented one or more features that
       require specific	attributes to be present. Conventions for attribute
       names that do not involve tool support should be	documented in
       appropriate user-level documentation. In	documenting attributes,	one
       additional distinction is made. Attributes that exist only as post-v5
       attribute/value pairs are referred to as	non-core attributes; older
       attributes (which may also be represented in core data structures) are
       referred	to as core attributes.

CORE ATTRIBUTES
       The following table lists all known core	BRL-CAD	attributes and
       aliases.	Any code setting or reading the	value of one of	these
       attributes must handle all aliases, to ensure all functions asking for
       the value in question get a consistent answer.

       Table 1.	Core Attributes
       +------------+-------------------------------------------------------------+-------------+
       |Property    | Attribute	Name(s)						  | Typical	|
       |	    |								  | Value(s)	|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Region	    | region	  | REGION	|	    |		    |	  | Yes, R or	|
       |Flag	    |		  |		|	    |		    |	  | 1		|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Region	    | region_id	  | REGION_ID	| id	    | ID	    |	  | -1,	0, and	|
       |Identifier  |		  |		|	    |		    |	  | positive	|
       |Number	    |		  |		|	    |		    |	  | integers	|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Material    | material_id | MATERIAL_ID	| GIFTmater | GIFT_MATERIAL | mat | 0 and	|
       |Identifier  |		  |		|	    |		    |	  | positive	|
       |Number	    |		  |		|	    |		    |	  | integers	|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Air Code    | air	  | AIR		| AIRCODE   |		    |	  | 0 or 1	|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Line Of	    | los	  | LOS		|	    |		    |	  |		|
       |Sight	    |		  |		|	    |		    |	  |		|
       |Thickness   |		  |		|	    |		    |	  |		|
       |Equivalence |		  |		|	    |		    |	  |		|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Color (Red  | color	  | rgb		| RGB	    | COLOR	    |	  | ###/###/###	|
       |Green Blue) |		  |		|	    |		    |	  |		|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Shader Name | oshader	  | SHADER	|	    |		    |	  | string	|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       |Inherit	    | inherit	  | INHERIT	|	    |		    |	  | Yes	or 1	|
       |Properties  |		  |		|	    |		    |	  |		|
       +------------+-------------+-------------+-----------+---------------+-----+-------------+
       Given the importance of these attributes, it is appropriate to briefly
       outline the meaning and purpose of each of them:

       Region Flag:
	   The Region Flag identifies a	particular geometric combination as
	   being a solid material - in other words, any	geometry below this
	   combination in the tree can overlap without the overlap being
	   regarded as a non-physical description, since it is the combination
	   of all descriptions in the region object that define	the physical
	   volume in space.

       Region ID Flag:
	   The Region ID Flag identifies a particular region with a unique
	   number. This	allows multiple	region objects to be regarded as being
	   the same type of region, without requiring that they	be included in
	   the same combination	object.

       Material	ID Number:
	   The Material	ID Number corresponds to an entry in a DENSITIES
	   table, usually contained in a text file. This table associates
	   numbers with	material names and density information,	used by
	   analytical programs such as rtweight.

       Air Flag:
	   The Air Flag	alerts the raytracer that the region in	question is
	   modeling air, which is handled by specialized rules in LIBRT.

       Line of Sight:

       Color:

       Shader Name:
	   LIBRT can utilize a variety of shaders when rendering - this
	   attribute holds a text string which corresponds to the name of the
	   shader to be	used.

       Inherit:

EXAMPLES
SEE ALSO
       attr(n).

AUTHOR
       BRL-CAD Team

BUG REPORTS
       Reports of bugs or problems should be submitted via electronic mail to
       <devs@brlcad.org>, or via the "cadbug.sh" script.

BRL-CAD				  07/08/2017		STANDARD ATTRIBUTES(5)

NAME | BACKGROUND | CORE ATTRIBUTES | EXAMPLES | SEE ALSO | AUTHOR | BUG REPORTS

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